All Solutions
Page 957: Practice Problems
$$
begin{align*}
L &= L_o sqrt{1 – dfrac{v^2}{c^2}} \
L &= 1.00 text{ m} sqrt{1 – dfrac{(0.999 c)^2}{c^2}} \
L &= 0.0447 m
end{align*}
$$
The length of the meterstick contracts as speed increases, if the speed is 0.999 c, the length of the meterstick is $boxed{text{0.0447 m}}$
textbf{0.0447 m}
$$
$$
l=1text{m}sqrt{1-0.999^2} = 0.0447text{ m}.
$$
$L = 2.00$ m
$v = 0.995 c$
$textbf{Find:}$ Length of the wood at rest, $L_o$
Using the length contraction formula, we can calculate $L_o$ as follows:
$$
begin{align*}
L_o &= dfrac{L}{sqrt{1 – dfrac{v^2}{c^2}}} \
L_o &= dfrac{2.00 text{ m}}{sqrt{1 – dfrac{(0.995c)^2}{c^2}}} \
L_o &= boxed{20 text{ m}}
end{align*}
$$
$$
l=l_0sqrt{1-0.995^2}
$$
and from here we obtain
$$
l_0=frac{l}{sqrt{1-0.995^2}} =20text{ m}
$$
The length contraction formula is given by
$$
begin{align}
L=L_0 sqrt{1-frac{v^2}{c^2}}
end{align}
$$
where $L$ is the length of the (one dimensional) object in a lab frame of reference, $L_0$ is the length of the object in a frame of reference in which the object is at rest, $v$ is the speed of the moving frame of reference and $c$ is the speed of light in vacuum.
The proper length of the meterstick $L_0$ is
$$
begin{align*}
L_0=1 text{m}
end{align*}
$$
The length of the meterstick in the laboratory frame of reference $L$ is
$$
begin{align*}
L=0.5 text{m}
end{align*}
$$
By using Eq. (1) we can express the speed of the meterstick $v$ as
$$
begin{align*}
frac{v^2}{c^2}&=1-frac{L^2}{L_0^2}\
&=1-frac{(0.5 text{m})^2}{(1 text{m})^2}\
&=0.75
end{align*}
$$
Thus, the speed of the meterstick $v$ is
$$
begin{align*}
boxed{v}&=sqrt{0.75}c\
&=boxed{0.86c}
end{align*}
$$
v=0.86c
$$